// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * IPv6 fragment reassembly for connection tracking
 *
 * Copyright (C)2004 USAGI/WIDE Project
 *
 * Author:
 *      Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
 *
 * Based on: net/ipv6/reassembly.c
 */

#define pr_fmt(fmt) "IPv6-nf: " fmt

#include <linux/errno.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/net.h>
#include <linux/netdevice.h>
#include <linux/ipv6.h>
#include <linux/slab.h>

#include <net/ipv6_frag.h>

#include <net/netfilter/ipv6/nf_conntrack_ipv6.h>
#include <linux/sysctl.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv6.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
#include <net/netns/generic.h>

static const char nf_frags_cache_name[] = "nf-frags";

static unsigned int nf_frag_pernet_id __read_mostly;
static struct inet_frags nf_frags;

static struct nft_ct_frag6_pernet *nf_frag_pernet(struct net *net)
{
        return net_generic(net, nf_frag_pernet_id);
}

#ifdef CONFIG_SYSCTL

static struct ctl_table nf_ct_frag6_sysctl_table[] = {
        {
                .procname       = "nf_conntrack_frag6_timeout",
                .maxlen         = sizeof(unsigned int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
        },
        {
                .procname       = "nf_conntrack_frag6_low_thresh",
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
        },
        {
                .procname       = "nf_conntrack_frag6_high_thresh",
                .maxlen         = sizeof(unsigned long),
                .mode           = 0644,
                .proc_handler   = proc_doulongvec_minmax,
        },
};

static int nf_ct_frag6_sysctl_register(struct net *net)
{
        struct nft_ct_frag6_pernet *nf_frag;
        struct ctl_table *table;
        struct ctl_table_header *hdr;

        table = nf_ct_frag6_sysctl_table;
        if (!net_eq(net, &init_net)) {
                table = kmemdup(table, sizeof(nf_ct_frag6_sysctl_table),
                                GFP_KERNEL);
                if (table == NULL)
                        goto err_alloc;
        }

        nf_frag = nf_frag_pernet(net);

        table[0].data   = &nf_frag->fqdir->timeout;
        table[1].data   = &nf_frag->fqdir->low_thresh;
        table[1].extra2 = &nf_frag->fqdir->high_thresh;
        table[2].data   = &nf_frag->fqdir->high_thresh;
        table[2].extra1 = &nf_frag->fqdir->low_thresh;

        hdr = register_net_sysctl_sz(net, "net/netfilter", table,
                                     ARRAY_SIZE(nf_ct_frag6_sysctl_table));
        if (hdr == NULL)
                goto err_reg;

        nf_frag->nf_frag_frags_hdr = hdr;
        return 0;

err_reg:
        if (!net_eq(net, &init_net))
                kfree(table);
err_alloc:
        return -ENOMEM;
}

static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
{
        struct nft_ct_frag6_pernet *nf_frag = nf_frag_pernet(net);
        const struct ctl_table *table;

        table = nf_frag->nf_frag_frags_hdr->ctl_table_arg;
        unregister_net_sysctl_table(nf_frag->nf_frag_frags_hdr);
        if (!net_eq(net, &init_net))
                kfree(table);
}

#else
static int nf_ct_frag6_sysctl_register(struct net *net)
{
        return 0;
}
static void __net_exit nf_ct_frags6_sysctl_unregister(struct net *net)
{
}
#endif

static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
                             struct sk_buff *prev_tail, struct net_device *dev,
                             int *refs);

static inline u8 ip6_frag_ecn(const struct ipv6hdr *ipv6h)
{
        return 1 << (ipv6_get_dsfield(ipv6h) & INET_ECN_MASK);
}

static void nf_ct_frag6_expire(struct timer_list *t)
{
        struct inet_frag_queue *frag = timer_container_of(frag, t, timer);
        struct frag_queue *fq;

        fq = container_of(frag, struct frag_queue, q);

        ip6frag_expire_frag_queue(fq->q.fqdir->net, fq);
}

/* Creation primitives. */
static struct frag_queue *fq_find(struct net *net, __be32 id, u32 user,
                                  const struct ipv6hdr *hdr, int iif)
{
        struct nft_ct_frag6_pernet *nf_frag = nf_frag_pernet(net);
        struct frag_v6_compare_key key = {
                .id = id,
                .saddr = hdr->saddr,
                .daddr = hdr->daddr,
                .user = user,
                .iif = iif,
        };
        struct inet_frag_queue *q;

        if (!(ipv6_addr_type(&hdr->daddr) & (IPV6_ADDR_MULTICAST |
                                            IPV6_ADDR_LINKLOCAL)))
                key.iif = 0;

        q = inet_frag_find(nf_frag->fqdir, &key);
        if (!q)
                return NULL;

        return container_of(q, struct frag_queue, q);
}


static int nf_ct_frag6_queue(struct frag_queue *fq, struct sk_buff *skb,
                             const struct frag_hdr *fhdr, int nhoff,
                             int *refs)
{
        unsigned int payload_len;
        struct net_device *dev;
        struct sk_buff *prev;
        int offset, end, err;
        u8 ecn;

        if (fq->q.flags & INET_FRAG_COMPLETE) {
                pr_debug("Already completed\n");
                goto err;
        }

        payload_len = ntohs(ipv6_hdr(skb)->payload_len);

        offset = ntohs(fhdr->frag_off) & ~0x7;
        end = offset + (payload_len -
                        ((u8 *)(fhdr + 1) - (u8 *)(ipv6_hdr(skb) + 1)));

        if ((unsigned int)end > IPV6_MAXPLEN) {
                pr_debug("offset is too large.\n");
                return -EINVAL;
        }

        ecn = ip6_frag_ecn(ipv6_hdr(skb));

        if (skb->ip_summed == CHECKSUM_COMPLETE) {
                const unsigned char *nh = skb_network_header(skb);
                skb->csum = csum_sub(skb->csum,
                                     csum_partial(nh, (u8 *)(fhdr + 1) - nh,
                                                  0));
        }

        /* Is this the final fragment? */
        if (!(fhdr->frag_off & htons(IP6_MF))) {
                /* If we already have some bits beyond end
                 * or have different end, the segment is corrupted.
                 */
                if (end < fq->q.len ||
                    ((fq->q.flags & INET_FRAG_LAST_IN) && end != fq->q.len)) {
                        pr_debug("already received last fragment\n");
                        goto err;
                }
                fq->q.flags |= INET_FRAG_LAST_IN;
                fq->q.len = end;
        } else {
                /* Check if the fragment is rounded to 8 bytes.
                 * Required by the RFC.
                 */
                if (end & 0x7) {
                        /* RFC2460 says always send parameter problem in
                         * this case. -DaveM
                         */
                        pr_debug("end of fragment not rounded to 8 bytes.\n");
                        inet_frag_kill(&fq->q, refs);
                        return -EPROTO;
                }
                if (end > fq->q.len) {
                        /* Some bits beyond end -> corruption. */
                        if (fq->q.flags & INET_FRAG_LAST_IN) {
                                pr_debug("last packet already reached.\n");
                                goto err;
                        }
                        fq->q.len = end;
                }
        }

        if (end == offset)
                goto err;

        /* Point into the IP datagram 'data' part. */
        if (!pskb_pull(skb, (u8 *) (fhdr + 1) - skb->data)) {
                pr_debug("queue: message is too short.\n");
                goto err;
        }
        if (pskb_trim_rcsum(skb, end - offset)) {
                pr_debug("Can't trim\n");
                goto err;
        }

        /* Note : skb->rbnode and skb->dev share the same location. */
        dev = skb->dev;
        /* Makes sure compiler wont do silly aliasing games */
        barrier();

        prev = fq->q.fragments_tail;
        err = inet_frag_queue_insert(&fq->q, skb, offset, end);
        if (err) {
                if (err == IPFRAG_DUP) {
                        /* No error for duplicates, pretend they got queued. */
                        kfree_skb_reason(skb, SKB_DROP_REASON_DUP_FRAG);
                        return -EINPROGRESS;
                }
                goto insert_error;
        }

        if (dev)
                fq->iif = dev->ifindex;

        fq->q.stamp = skb->tstamp;
        fq->q.tstamp_type = skb->tstamp_type;
        fq->q.meat += skb->len;
        fq->ecn |= ecn;
        if (payload_len > fq->q.max_size)
                fq->q.max_size = payload_len;
        add_frag_mem_limit(fq->q.fqdir, skb->truesize);

        /* The first fragment.
         * nhoffset is obtained from the first fragment, of course.
         */
        if (offset == 0) {
                fq->nhoffset = nhoff;
                fq->q.flags |= INET_FRAG_FIRST_IN;
        }

        if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
            fq->q.meat == fq->q.len) {
                unsigned long orefdst = skb->_skb_refdst;

                skb->_skb_refdst = 0UL;
                err = nf_ct_frag6_reasm(fq, skb, prev, dev, refs);
                skb->_skb_refdst = orefdst;

                /* After queue has assumed skb ownership, only 0 or
                 * -EINPROGRESS must be returned.
                 */
                return err ? -EINPROGRESS : 0;
        }

        skb_dst_drop(skb);
        skb_orphan(skb);
        return -EINPROGRESS;

insert_error:
        inet_frag_kill(&fq->q, refs);
err:
        skb_dst_drop(skb);
        return -EINVAL;
}

/*
 *      Check if this packet is complete.
 *
 *      It is called with locked fq, and caller must check that
 *      queue is eligible for reassembly i.e. it is not COMPLETE,
 *      the last and the first frames arrived and all the bits are here.
 */
static int nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *skb,
                             struct sk_buff *prev_tail, struct net_device *dev,
                             int *refs)
{
        void *reasm_data;
        int payload_len;
        u8 ecn;

        inet_frag_kill(&fq->q, refs);

        ecn = ip_frag_ecn_table[fq->ecn];
        if (unlikely(ecn == 0xff))
                goto err;

        reasm_data = inet_frag_reasm_prepare(&fq->q, skb, prev_tail);
        if (!reasm_data)
                goto err;

        payload_len = -skb_network_offset(skb) -
                       sizeof(struct ipv6hdr) + fq->q.len -
                       sizeof(struct frag_hdr);
        if (payload_len > IPV6_MAXPLEN) {
                net_dbg_ratelimited("nf_ct_frag6_reasm: payload len = %d\n",
                                    payload_len);
                goto err;
        }

        /* We have to remove fragment header from datagram and to relocate
         * header in order to calculate ICV correctly. */
        skb_network_header(skb)[fq->nhoffset] = skb_transport_header(skb)[0];
        memmove(skb->head + sizeof(struct frag_hdr), skb->head,
                (skb->data - skb->head) - sizeof(struct frag_hdr));
        skb->mac_header += sizeof(struct frag_hdr);
        skb->network_header += sizeof(struct frag_hdr);

        skb_reset_transport_header(skb);

        inet_frag_reasm_finish(&fq->q, skb, reasm_data, false);

        skb->ignore_df = 1;
        skb->dev = dev;
        ipv6_hdr(skb)->payload_len = htons(payload_len);
        ipv6_change_dsfield(ipv6_hdr(skb), 0xff, ecn);
        IP6CB(skb)->frag_max_size = sizeof(struct ipv6hdr) + fq->q.max_size;
        IP6CB(skb)->flags |= IP6SKB_FRAGMENTED;

        /* Yes, and fold redundant checksum back. 8) */
        if (skb->ip_summed == CHECKSUM_COMPLETE)
                skb->csum = csum_partial(skb_network_header(skb),
                                         skb_network_header_len(skb),
                                         skb->csum);

        fq->q.rb_fragments = RB_ROOT;
        fq->q.fragments_tail = NULL;
        fq->q.last_run_head = NULL;

        return 0;

err:
        inet_frag_kill(&fq->q, refs);
        return -EINVAL;
}

/*
 * find the header just before Fragment Header.
 *
 * if success return 0 and set ...
 * (*prevhdrp): the value of "Next Header Field" in the header
 *              just before Fragment Header.
 * (*prevhoff): the offset of "Next Header Field" in the header
 *              just before Fragment Header.
 * (*fhoff)   : the offset of Fragment Header.
 *
 * Based on ipv6_skip_hdr() in net/ipv6/exthdr.c
 *
 */
static int
find_prev_fhdr(struct sk_buff *skb, u8 *prevhdrp, int *prevhoff, int *fhoff)
{
        u8 nexthdr = ipv6_hdr(skb)->nexthdr;
        const int netoff = skb_network_offset(skb);
        u8 prev_nhoff = netoff + offsetof(struct ipv6hdr, nexthdr);
        int start = netoff + sizeof(struct ipv6hdr);
        int len = skb->len - start;
        u8 prevhdr = NEXTHDR_IPV6;

        while (nexthdr != NEXTHDR_FRAGMENT) {
                struct ipv6_opt_hdr hdr;
                int hdrlen;

                if (!ipv6_ext_hdr(nexthdr)) {
                        return -1;
                }
                if (nexthdr == NEXTHDR_NONE) {
                        pr_debug("next header is none\n");
                        return -1;
                }
                if (len < (int)sizeof(struct ipv6_opt_hdr)) {
                        pr_debug("too short\n");
                        return -1;
                }
                if (skb_copy_bits(skb, start, &hdr, sizeof(hdr)))
                        BUG();
                if (nexthdr == NEXTHDR_AUTH)
                        hdrlen = ipv6_authlen(&hdr);
                else
                        hdrlen = ipv6_optlen(&hdr);

                prevhdr = nexthdr;
                prev_nhoff = start;

                nexthdr = hdr.nexthdr;
                len -= hdrlen;
                start += hdrlen;
        }

        if (len < 0)
                return -1;

        *prevhdrp = prevhdr;
        *prevhoff = prev_nhoff;
        *fhoff = start;

        return 0;
}

int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
{
        u16 savethdr = skb->transport_header;
        u8 nexthdr = NEXTHDR_FRAGMENT;
        int fhoff, nhoff, ret;
        struct frag_hdr *fhdr;
        struct frag_queue *fq;
        struct ipv6hdr *hdr;
        int refs = 0;
        u8 prevhdr;

        /* Jumbo payload inhibits frag. header */
        if (ipv6_hdr(skb)->payload_len == 0) {
                pr_debug("payload len = 0\n");
                return 0;
        }

        if (find_prev_fhdr(skb, &prevhdr, &nhoff, &fhoff) < 0)
                return 0;

        /* Discard the first fragment if it does not include all headers
         * RFC 8200, Section 4.5
         */
        if (ipv6frag_thdr_truncated(skb, fhoff, &nexthdr)) {
                pr_debug("Drop incomplete fragment\n");
                return 0;
        }

        if (!pskb_may_pull(skb, fhoff + sizeof(*fhdr)))
                return -ENOMEM;

        skb_set_transport_header(skb, fhoff);
        hdr = ipv6_hdr(skb);
        fhdr = (struct frag_hdr *)skb_transport_header(skb);

        rcu_read_lock();
        fq = fq_find(net, fhdr->identification, user, hdr,
                     skb->dev ? skb->dev->ifindex : 0);
        if (fq == NULL) {
                rcu_read_unlock();
                pr_debug("Can't find and can't create new queue\n");
                return -ENOMEM;
        }

        spin_lock_bh(&fq->q.lock);

        ret = nf_ct_frag6_queue(fq, skb, fhdr, nhoff, &refs);
        if (ret == -EPROTO) {
                skb->transport_header = savethdr;
                ret = 0;
        }

        spin_unlock_bh(&fq->q.lock);
        rcu_read_unlock();
        inet_frag_putn(&fq->q, refs);
        return ret;
}
EXPORT_SYMBOL_GPL(nf_ct_frag6_gather);

static int nf_ct_net_init(struct net *net)
{
        struct nft_ct_frag6_pernet *nf_frag  = nf_frag_pernet(net);
        int res;

        res = fqdir_init(&nf_frag->fqdir, &nf_frags, net);
        if (res < 0)
                return res;

        nf_frag->fqdir->high_thresh = IPV6_FRAG_HIGH_THRESH;
        nf_frag->fqdir->low_thresh = IPV6_FRAG_LOW_THRESH;
        nf_frag->fqdir->timeout = IPV6_FRAG_TIMEOUT;

        res = nf_ct_frag6_sysctl_register(net);
        if (res < 0)
                fqdir_exit(nf_frag->fqdir);
        return res;
}

static void nf_ct_net_pre_exit(struct net *net)
{
        struct nft_ct_frag6_pernet *nf_frag  = nf_frag_pernet(net);

        fqdir_pre_exit(nf_frag->fqdir);
}

static void nf_ct_net_exit(struct net *net)
{
        struct nft_ct_frag6_pernet *nf_frag  = nf_frag_pernet(net);

        nf_ct_frags6_sysctl_unregister(net);
        fqdir_exit(nf_frag->fqdir);
}

static struct pernet_operations nf_ct_net_ops = {
        .init           = nf_ct_net_init,
        .pre_exit       = nf_ct_net_pre_exit,
        .exit           = nf_ct_net_exit,
        .id             = &nf_frag_pernet_id,
        .size           = sizeof(struct nft_ct_frag6_pernet),
};

static const struct rhashtable_params nfct_rhash_params = {
        .head_offset            = offsetof(struct inet_frag_queue, node),
        .hashfn                 = ip6frag_key_hashfn,
        .obj_hashfn             = ip6frag_obj_hashfn,
        .obj_cmpfn              = ip6frag_obj_cmpfn,
        .automatic_shrinking    = true,
};

int nf_ct_frag6_init(void)
{
        int ret = 0;

        nf_frags.constructor = ip6frag_init;
        nf_frags.destructor = NULL;
        nf_frags.qsize = sizeof(struct frag_queue);
        nf_frags.frag_expire = nf_ct_frag6_expire;
        nf_frags.frags_cache_name = nf_frags_cache_name;
        nf_frags.rhash_params = nfct_rhash_params;
        ret = inet_frags_init(&nf_frags);
        if (ret)
                goto out;
        ret = register_pernet_subsys(&nf_ct_net_ops);
        if (ret)
                inet_frags_fini(&nf_frags);

out:
        return ret;
}

void nf_ct_frag6_cleanup(void)
{
        unregister_pernet_subsys(&nf_ct_net_ops);
        inet_frags_fini(&nf_frags);
}